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//===- llvm/MC/MCAsmBackend.h - MC Asm Backend ------------------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_MC_MCASMBACKEND_H

#define LLVM_MC_MCASMBACKEND_H

#include "llvm/ADT/ArrayRef.h"

#include "llvm/MC/MCDirectives.h"

#include "llvm/MC/MCFixup.h"

#include "llvm/Support/Endian.h"

#include <cstdint>

namespace llvm {

class MCAlignFragment;

class MCDwarfCallFrameFragment;

class MCDwarfLineAddrFragment;

class MCFragment;

class MCRelaxableFragment;

class MCSymbol;

class MCAsmLayout;

class MCAssembler;

class MCCFIInstruction;

struct MCFixupKindInfo;

class MCInst;

class MCObjectStreamer;

class MCObjectTargetWriter;

class MCObjectWriter;

class MCSubtargetInfo;

class MCValue;

class raw_pwrite_stream;

class StringRef;

class raw_ostream;

/// Generic interface to target specific assembler backends.

class MCAsmBackend {

protected: // Can only create subclasses.

  MCAsmBackend(support::endianness Endian);

public:

  MCAsmBackend(const MCAsmBackend &) = delete;

  MCAsmBackend &operator=(const MCAsmBackend &) = delete;

  virtual ~MCAsmBackend();

  const support::endianness Endian;

  /// Return true if this target might automatically pad instructions and thus

  /// need to emit padding enable/disable directives around sensative code.

  virtual bool allowAutoPadding() const { return false; }

  /// Return true if this target allows an unrelaxable instruction to be

  /// emitted into RelaxableFragment and then we can increase its size in a

  /// tricky way for optimization.

  virtual bool allowEnhancedRelaxation() const { return false; }

  /// Give the target a chance to manipulate state related to instruction

  /// alignment (e.g. padding for optimization), instruction relaxablility, etc.

  /// before and after actually emitting the instruction.

  virtual void emitInstructionBegin(MCObjectStreamer &OS, const MCInst &Inst,

                                    const MCSubtargetInfo &STI) {}

  virtual void emitInstructionEnd(MCObjectStreamer &OS, const MCInst &Inst) {}

  /// lifetime management

  virtual void reset() {}

  /// Create a new MCObjectWriter instance for use by the assembler backend to

  /// emit the final object file.

  std::unique_ptr<MCObjectWriter>

  createObjectWriter(raw_pwrite_stream &OS) const;

  /// Create an MCObjectWriter that writes two object files: a .o file which is

  /// linked into the final program and a .dwo file which is used by debuggers.

  /// This function is only supported with ELF targets.

  std::unique_ptr<MCObjectWriter>

  createDwoObjectWriter(raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS) const;

  virtual std::unique_ptr<MCObjectTargetWriter>

  createObjectTargetWriter() const = 0;

  /// \name Target Fixup Interfaces

  /// @{

  /// Get the number of target specific fixup kinds.

  virtual unsigned getNumFixupKinds() const = 0;

  /// Map a relocation name used in .reloc to a fixup kind.

  virtual std::optional<MCFixupKind> getFixupKind(StringRef Name) const;

  /// Get information on a fixup kind.

  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;

  /// Hook to check if a relocation is needed for some target specific reason.

  virtual bool shouldForceRelocation(const MCAssembler &Asm,

                                     const MCFixup &Fixup,

                                     const MCValue &Target) {

    return false;

  }

  /// Hook to check if extra nop bytes must be inserted for alignment directive.

  /// For some targets this may be necessary in order to support linker

  /// relaxation. The number of bytes to insert are returned in Size.

  virtual bool shouldInsertExtraNopBytesForCodeAlign(const MCAlignFragment &AF,

                                                     unsigned &Size) {

    return false;

  }

  /// Hook which indicates if the target requires a fixup to be generated when

  /// handling an align directive in an executable section

  virtual bool shouldInsertFixupForCodeAlign(MCAssembler &Asm,

                                             const MCAsmLayout &Layout,

                                             MCAlignFragment &AF) {

    return false;

  }

  virtual bool evaluateTargetFixup(const MCAssembler &Asm,

                                   const MCAsmLayout &Layout,

                                   const MCFixup &Fixup, const MCFragment *DF,

                                   const MCValue &Target, uint64_t &Value,

                                   bool &WasForced) {

    llvm_unreachable("Need to implement hook if target has custom fixups");

  }

  /// Apply the \p Value for given \p Fixup into the provided data fragment, at

  /// the offset specified by the fixup and following the fixup kind as

  /// appropriate. Errors (such as an out of range fixup value) should be

  /// reported via \p Ctx.

  /// The  \p STI is present only for fragments of type MCRelaxableFragment and

  /// MCDataFragment with hasInstructions() == true.

  virtual void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,

                          const MCValue &Target, MutableArrayRef<char> Data,

                          uint64_t Value, bool IsResolved,

                          const MCSubtargetInfo *STI) const = 0;

  /// @}

  /// \name Target Relaxation Interfaces

  /// @{

  /// Check whether the given instruction may need relaxation.

  ///

  /// \param Inst - The instruction to test.

  /// \param STI - The MCSubtargetInfo in effect when the instruction was

  /// encoded.

  virtual bool mayNeedRelaxation(const MCInst &Inst,

                                 const MCSubtargetInfo &STI) const {

    return false;

  }

  /// Target specific predicate for whether a given fixup requires the

  /// associated instruction to be relaxed.

  virtual bool fixupNeedsRelaxationAdvanced(const MCFixup &Fixup, bool Resolved,

                                            uint64_t Value,

                                            const MCRelaxableFragment *DF,

                                            const MCAsmLayout &Layout,

                                            const bool WasForced) const;

  /// Simple predicate for targets where !Resolved implies requiring relaxation

  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,

                                    const MCRelaxableFragment *DF,

                                    const MCAsmLayout &Layout) const = 0;

  /// Relax the instruction in the given fragment to the next wider instruction.

  ///

  /// \param [out] Inst The instruction to relax, which is also the relaxed

  /// instruction.

  /// \param STI the subtarget information for the associated instruction.

  virtual void relaxInstruction(MCInst &Inst,

                                const MCSubtargetInfo &STI) const {};

  virtual bool relaxDwarfLineAddr(MCDwarfLineAddrFragment &DF,

                                  MCAsmLayout &Layout, bool &WasRelaxed) const {

    return false;

  }

  virtual bool relaxDwarfCFA(MCDwarfCallFrameFragment &DF, MCAsmLayout &Layout,

                             bool &WasRelaxed) const {

    return false;

  }

  /// @}

  /// Returns the minimum size of a nop in bytes on this target. The assembler

  /// will use this to emit excess padding in situations where the padding

  /// required for simple alignment would be less than the minimum nop size.

  ///

  virtual unsigned getMinimumNopSize() const { return 1; }

  /// Returns the maximum size of a nop in bytes on this target.

  ///

  virtual unsigned getMaximumNopSize(const MCSubtargetInfo &STI) const {

    return 0;

  }

  /// Write an (optimal) nop sequence of Count bytes to the given output. If the

  /// target cannot generate such a sequence, it should return an error.

  ///

  /// \return - True on success.

  virtual bool writeNopData(raw_ostream &OS, uint64_t Count,

                            const MCSubtargetInfo *STI) const = 0;

  /// Give backend an opportunity to finish layout after relaxation

  virtual void finishLayout(MCAssembler const &Asm,

                            MCAsmLayout &Layout) const {}

  /// Handle any target-specific assembler flags. By default, do nothing.

  virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}

  /// Generate the compact unwind encoding for the CFI instructions.

  virtual uint32_t

      generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {

    return 0;

  }

  /// Check whether a given symbol has been flagged with MICROMIPS flag.

  virtual bool isMicroMips(const MCSymbol *Sym) const {

    return false;

  }

};

} // end namespace llvm

#endif // LLVM_MC_MCASMBACKEND_H